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Discussion

The graph on the left shows the relation between energy and acousticness in the songs by U2 from before 1990 and the graph on the right does the same for the 90’s period. This showcases that the experimental phase of U2 in the 90’s goes hand in hand with a decrease in overall acousticness, whilst maintaining the energy present in their earlier work. The outlier on the bottom right is a song called ‘The First Time’. I have chosen to limit these plots to the songs before 2000, as their 2000 album ‘All that you can’t leave behind’ (featuring smash hit ‘Beautiful day’) meant a return to their style from the 80’s after ‘POP’ (1997), their most dissapointing album in terms of sales and reviews.

The reason for the return to their old style after the turn of the century has everything to do with the struggles of the band in the 90’s, which came from their will to innovate and ‘move with the times’ (although I think they just had a bit of an identity crisis). Comparing the pre 1990 and post 1990 period in a computational manner will shed a light on the most extensive differences between the two periods, which I will relate to the consequences this had for the band and their music going forward.

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Chroma Analysis

On this page I showcase the chroma features of three different tracks by U2, to delve a bit deeper into the harmonic structure of some of their songs in different periods. I have chosen:

‘The First Time’ (Key: G# major), an outlier track from the 90s which displays a combination of low energy and high acousticness that is unusual for their music from that period. The chromagram shows high magnitude in the G#, a bit in C (harmonic third), and most explicitly the D# (harmonic 5th), which is logical as D#major is the most prevalent chord in the song, and theres also significant harmonics coming from the root chord G#major. Furthermore it is quite monotone in its harmonic structure, in contrast to the track ‘Mofo’ on its right, which is from the same period but radically different.

‘Mofo’, produced by synthpop producer Mark Ellis (aka Flood) is an eclectic, high energy song which has an acousticness of near zero (understandably). It is very representative of the artistic turn U2 took in the 90’s embracing dance and disco whilst leaving the elements that made them famous in the 80’s behind. The use of modulating, distorted synths and the fast tempo of the song atrribute to its energy and acousticness rating, but are also reflected in the chromagram which is a bit all over the place, as it struggles with these effects.

‘With or Without You’, one of their most iconic songs from the ‘Joshua Tree’ Album (1987) which is on the lower end of the energy spectrum in comparison to many of the other tracks and displays a low acousticness according to the Spotify API, even though it doesn’t exactly feel that way. Synths, the use of reverb and other forms of FX likely contribute to this. This was quite innovative for the time period and was a consequence of the moving and renovating of windmill lane studios in Dublin. This was done explicitly to accomodate the technology and capacity required for the ambitions U2 had with the Joshua Tree album. The chromagram shows that this song has a clear key (D major) and harmonic structure which doesn’t fluctuate too much. This makes it an excellent example to be set against ‘Mofo’.

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Loudness and Timbre

The Cepstogram (or ‘Timbregram’) on the right showcases the Timbre features of one of U2’s most well known songs: ‘One’ (1991) from the album ‘Achtung Baby’. This album showcases the transition between their early work and their experimental phase in the 90’s. It also provides the only number 1 hit they score in this period, which ironically is closest to their earlier work as well. ‘One’ has quite a standard structure: (V-CH-V2-CH2-V3-CH3-B-Ch4-Outtro) but increases in energy exponentially towards the climax where singer Bono exclaims ’Higher! (Baby). This is represented very well in the cepstogram, where timbre feature c01 (loudness) increases in magnitude all the way through to the end.

We also see an increase in magnitude on c05 (Standard pitch deviation). This is likely due to the Edge’s (guitarist) riffs. Although they are simple from a musicians perspective, they do create a level of harmonic complexity which causes the increase in magnitude. Around 50sec and 110sec, this guitar makes room for a more staccato use of chords, explaining the slight decrease in magnitude at this point. The Edge uses a fat guitar sound with slight echo and delay, which creates his iconic sound.

The harmonic content (co6) has a low magnitude, which is logical from a musicians perspective (like I mentioned earlier) because many of the harmonic patterns are continuously repeated throughout the song. An explanation as to why the magnitude drops as the song progresses could be that the harmonic content becomes more noisy and muddy as the loudness increases, making unique instruments less able to stand out amongst the rest.

Many of the disco tracks of the 90’s are represented by synth basses and electronic instruments that operate on the low end of the frequency spectrum. The spectral rolloff (c11) and spectral centroid (c07) values indicate that ‘One’ does not operate in this part of the spectrum too much, meaning the noise and muddiness as indicated by c06 aren’t (primarily) caused by this phenomenon.

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Temporal comparisons

For my temporal comparisons I have chosen the 2 tracks with the highest energy values from both periods (according to the scatter plot on the track features page). They are also both over 5 minutes, making them, to an extent, equals in their own time periods.

Although the tempo of both of these tracks is high, it does not exceed the allegretto domain (112-124BPM). This is logical for ‘Surrender’, which comes from the album ‘War’ (1983) and still exists within the post-punk/new wave era of the band. Mofo (120BPM), being their highest energy song from the 90’s, showcases that they embraced the disco genre (which is characterised by a BPM between 110-135).

One can also see that although the tempo of both tracks is constant, ‘Surrender’ has a much thicker and more winding line running across the tempogram. This can be attributed to the recording of more live instruments (especially drums and bass). One can conclude that a metronome was most likely used for the recording, although this tempogram shows that when all instruments are actually played and recorded by musicians, the song is more ‘alive’ and does not adhere to the strict tempo of an electronic beat.

The BPM line for ‘Mofo’, however, is as straight as it gets with only mild variations, as I’ll explain below.

To go a bit deeper into both songs/tempograms:

Mofo

Mofo is based around a sample from the 1970 disco hit “Funky Nassau” by the Bahama Soul Stew. Although the beat and rhythm of the track are very reminiscent of 90’s disco, it’s the structure of the track which connects it to U2’s characteristic rock style. The song tempo is 120 BPM, but shows significant tempo deviations/harmonics towards the middle and ending of the song. At 2:43, the drums completely dissappear and they only pick up again around 3:00, which explains the deviation there. Towards the end of the song something interesting happens, as the guitar starts playing 16th notes off-sync to the beat, creating what I like to call a ‘rotary spacious feeling’, almost like a helicopter (this is caused by offset delays on the guitar). I find it very interesting that the spectogram recognises this as a rhythmical element.

Surrender

The song tempo is a pretty steady 117 BPM but the tempogram shows one deviation between 2:35 - 2:50, which is when the snaredrum drops out and a break of sorts occurs, disrupting the pattern displayed in the drums throughout the rest of the song. Although the tempo doesn’t change this does throw off the computation, as can be seen by the vertical line around the middle of the tempogram.

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CLustering Heatmaps

The interactive heatmaps on the right side show both the playlists within my corpus clustered together based on some of the Spotify API’s track feature classifications.

The left heatmap showcases the playlist of songs by U2 before 1990. When listening to the songs from top to bottom, the intensity and energy of the songs increases. Songs like ‘Freedom for my people’ (just 1 guitar) and ‘October’ (just a piano) are nicely clustered together, whilst the more adventurous, ‘heavy’ recordings are grouped at the bottom.

For the heatmap on the right, the songs are ordered in a similar manner. Here we find the most energetic and ‘disco-like’ songs at the top, and the more low-energy acoustic songs at the bottom.